The cucurbit family includes a number of valuable crop species (melon, cucumber, squash/pumpkin, watermelon, et al.). Production of cucurbit crops in large quantities is important worldwide, since cucurbits are important commercially in many regions, and are increasingly available throughout the year. According to Food and Agriculture Organization (FAO, 2002), world production of watermelon exceeded 80 million tons worldwide; cucumber exceeded 36 million tons; melon exceeded 22 million tons, and squash exceeded 17 million tons.
However, a wide range of pathogens (virus, fungi, bacteria, nematodes, and insects) affects productivity of cucurbits (Blanchard et al., 1994, A color atlas of cucurbit diseases, New York: Manson Publishing/John Wiley; Zitter et al., 1996 Compendium of cucurbit diseases. St Paul, Minn.: APS Press). Among these, virus diseases of cucurbits are an important limitation in production. Massive damage up to total loss can be caused by virus, which prevents the growth of some cucurbit crops in certain area. Cucurbits are susceptible to many viruses from several virus families and virus resistance is therefore of major agricultural importance (Provvidenti, 1993, Resistance to viral disease of cucurbits. In: Kyle, M. M., ed. Resistance to viral diseases of vegetables. Portland, Oreg.: Timber Press; 1993:8-43).
The genus Tospovirus (Bunyaviridae) (9, 18) includes some of the most important plant viruses causing severe diseases in agricultural, ornamental, and horticultural, crops (16, 26, 34, 100). The type member of the genus is Tomato spotted wilt virus (TSWV; 20).
Cucurbit-infecting Tospovirus spp. have been identified in different countries since the 1980s, particularly in South America and Asia. Two cucurbit-infecting Tospovirus spp. are included in the list of the species accepted by the International Committee on Taxonomy of Viruses (ICTV): Watermelon silver mottle virus (WSMoV), originally reported on Citrullus lanatus in Okinawa, Japan in 1982 and in 1992 in Taiwan (40); and Zucchini lethal chlorosis virus (ZLCV), reported on Cucurbita pepo in Brazil in 1999 (1). In addition, two tentative species from cucurbits have been proposed: Watermelon bud necrosis virus (WBNV), reported on cucurbits in India (13); and, more recently, Melon yellow spot virus (MYSV) on netted melon in Japan and Thailand (14; 101).
A novel Tospovirus (Bunyaviridae) species was recently isolated (Ciuffo et al., “A New Tospovius sp. in Cucurbit Crops in Mexico”, Plant Disease, May 2009, 93(5):467-474). In the state of Guerrero, Mexico, several honeydew melon (Cucumis melo) plants exhibiting mosaic, leaf blistering, leaf deformation, and fruit splitting were observed. Electron-microscopic analysis of leaf-dip extracts showed only particles with the morphological features of viruses of the Tospovirus genus. Biological, serological, and molecular properties and phylogenetic analysis showed that this Tospovirus sp. is a new and distinct species in the genus Tospovirus and is tentatively named Melon Severe Mosaic Virus MeSMV). Subsequent surveys showed its widespread occurrence in cucurbit crops in Mexico. Methods of screening plants for resistance, tolerance or susceptibility to such virus; and methods of producing plants resistant or tolerant to such virus are provided herein.